There are two major categories in the structure of conventional switches used in operation panels.
The structure shown in FIG. 12, a cross sectional view, and FIG. 13, an exploded perspective view, belongs to category one. On an insulating substrate 1 of the switch, a pattern of fixed contact points 2 is formed, which consists of an outer contact point 2A of ring shape and an inner contact point 2B disposed in the center of the ring shape. The inner contact point 2B is provided with a lead portion 2C, which runs through a cut 2D formed in the outer contact point 2A. An insulation layer 3 is provided on the lead portion 2C and the cut 2D, and a movable contact point 4 of round dome shape made of an elastic thin metal sheet is placed on the outer contact point 2A. A flexible insulating film 5 having an adhesive agent 5A on the bottom surface is provided over the above described structure, and the movable contact point 4 and the insulating substrate 1 are fixed together thereby.
The structure of a category two switch is shown in FIG. 14, a cross sectional view, and FIG. 15, an exploded perspective view. The switch comprises an insulating substrate 6, on which a pattern of fixed contact points 7 is formed. The pattern consists of an outer contact point 7A of ring shape and an inner contact point 7B disposed in the center of the ring shape. The inner contact point 7B is provided with a through hole 7C. The inner contact point 7B is connected to the reverse surface of the insulating substrate 6 via the through hole 7C provided at the center. A movable contact point 4 of round dome shape made of an elastic thin metal plate is placed on the outer contact point 7A. A flexible insulating film 5 having an adhesive agent 5A on the bottom surface is provided over the above described structure, and the movable contact point 4 and insulating substrate 6 are fixed together thereby.
In the switches of either category, a press given to the movable contact point 4 of round dome shape at the center causes an elastic inversion with the movable contact point 4, which brings the bottom center into making contact with the inner contact point 2B (or 7B). The outer contact point 2A and the inner contact point 2B (or the outer contact point 7A and the inner contact point 7B) are thus short-circuited to generate an ON state in the switch.
Recently, along with the general trend of down-sizing among the electronic apparatus, it has been requested for the operation panels as well as the switches incorporated therein to have smaller dimensions. In order to down-size the switches of above described conventional structure, basically the dimensions have to be reduced with respect to each of the constituent parts and components. However, the range of dimensional dispersion that arises during processing of the constituent parts and components remains unchanged. Therefore, the size of inner contact point 2B, or 7B, on which the movable contact point 4 of round dome shape comes to make contact as a result of the elastic inversion, can not be reduced for a substantial extent; among those elements of fixed contact point 2, or 7, pattern-formed on the insulating substrate 1, or 6. This makes it difficult to form the outer contact point 2A, or 7A, around the inner contact point preserving a certain specific insulation gap in dimensions that can insure a stable contact. This is a limitation posed to the down-sizing effort.
Furthermore, the second category switches are costly because they need connection by wiring in the bottom surface of insulating substrate 6. In addition, a subtle difference may arise with the category two switches in the quantity of switching stroke and the feeling of operation, depending on whether the center bottom of the inverted movable contact point 4 makes contact with the small-diameter fixed contact point 7 at a point precisely coincidental to the through hole 7C, or not.
The present invention aims to offer a switch that provides a stable contact performance and a superior feeling of operation even in a down-sized configuration.